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Application Requiring 50% Capacity Reductions
— This is
the usual specification for heat pump applications and should
cover majority of cases. The necessary modifications to com-
pressor capacity control can be accomplished by ordering the
compressor with factory modifications and then completing
modification at the jobsite with field-supplied components.
Factory Modifications — The compressor order should state
that compressor is to be special for heat pump application, and
is to include only enough unloader power elements to unload
the compressor down to 50% displacement. The unloaded
cylinders will be those closest to pump end of the compressor.
Field Completion — Install a
1
/
4
-in. or
3
/
8
-in. bypass line
between the control oil pressure connection and the crankcase
and install a solenoid valve in this line.
The cylinders set up for unloading may be loaded or unload-
ed by operation of this solenoid valve. When the solenoid valve
is closed, full oil pressure is available to the controlled
cylinders and these will be loaded so that compressor will be
operating on 100% capacity. When the solenoid valve is open,
oil pressure will be bled from the controlled cylinders and they
will be unloaded, so that compressor will then be operating at
50% capacity. A 2-step thermostat controlling the compressor
can thus utilize 2 capacity steps by operating the compressor
starter and solenoid bypass valve.
Application Requiring More Than One Step of Capacity
Reduction — This can be furnished on special order for com-
pressors having 6, 8, or 12 cylinders. Arrangement consists of
furnishing a compressor with external solenoid unloading type
capacity control. The control can be furnished with or without
3-way valves (Table 18).
Table 18 — Capacity Control Steps and
Heat Pump Modification
Hot Gas Bypass —
Hot gas bypass may be required on
some systems for one of the following reasons:
1. Frequent operation at loads below minimum capacity
(compressor fully unloaded).
2. To avoid low-load compressor cycling on the low-
pressure switch. Excessive cycling can reduce equipment
life and increase demand charges.
3. Specifications call for hot gas bypass (better humidity
control, etc.).
COMPRESSOR
EXTERNAL
3-WAY
SOLENOID
VALVES
AVAILABLE
CAPACITY STEPS
(%)
5F40, 5H40, 5H46
3 100, 75, 50, 25
5F60, 5H60, 5H66
4 100, 83.3, 66.7, 50, 33.3
5H80
4 100, 87.5, 62.5, 37.5, 25
5H120, 5H126
4 100, 83.3, 66.7, 50, 33.3
CAPACITY CONTROL VALVE
SURGE CHAMBER
HYDRAULIC RELAY
REMOVE THESE ALLEN
HEAD SCREWS TO
REMOVE HYDRAULIC
RELAY.
MAGNETIC PLUG
(PUMP INTAKE)
4
2
3
1
OIL PUMP PRESSURE
(AFTER FILTERING)
UNLOADER SEQUENCE 1/8” NPT CONNECTION.
OIL PRESSURE LOAD THESE STEPS.
TO UNLOAD, DUMP CONTROL OIL BACK INTO OIL
RESERVOIR THROUGH CRANKCASE & OIL FILL
CONNECTION.
OIL PUMP PRESS
(BEFORE FILTERING)
FULL FLOW
FILTER HOUSING
3-WAY SOLENOID VALVES
SEE FIG. 13 FOR RECOMMENDED OPERATION.
UL
#2
UL
#1
UL
#3
UL
#4
CRANKCASE
& OIL FILL
CONNECTION
1/8” NPT
Fig. 16 — 5H120 and 126 Bearing Head Assembly